Stabilization of polyaldehydes with benzothiazole and derivatives thereof



United States Patent 3,262,907 STABILIZATION 0F POLYALDEHYDES WITHBENZOTHIAZOLE AND DERIVA- TIVES THEREOF Eli Perry, Galveston, Tex.,assignor to Monsanto Company, a corporation of Delaware No Drawing.Filed Sept. 20, 1962, Ser. No. 225,160 5 Claims. (Cl. 26045.8)

The present invention relates to high polymers of aldehydes and moreparticularly to stabilization of such polymers.

It is known that ald'ehydes such as acetaldehyde, propionaldehyde,acrolein, methacrolein and substituted methacroleins, and the like canbe polymerized to yield acetal-type polymers of high molecular weighthaving molecular chains consisting of a succession of alternate carbonatoms and oxygen atoms as represented by the structural formula at theends of the polymer molecules; thermal decomposition at elevatedtemperatures with reformation of the monomeric aldehyde; oxidativeattack by oxygen or free radicals having an oxidative tendency; and acidcleavage often brought about by residual traces of the acid catalystemployed in the preparation of the polymer.

Stabilization of the polyaldehydes can be effected by reacting thepolymers to tie up the end groups. For example, the polymers can beesterified by reacting them with carboxylic acid anhydrides, preferablyacetic anhydride, in the presence of acid-binding substances. Theseprocesses, however, are complicated and expensive. Another method ofprotecting polymeric materials against attack is by the addition oforganic compounds as stabilizers. In practice, however, it has been hardto achieve stabilization of polyaldehydes by this method althoughcertain classes of organic compounds have been found to be effectivewith formaldehyde polymers, i.e., polyoxymethylene compounds.Consequently, it is an object of the present invention to provide anovel class of stabilizers which can be incorporated into polyaldehydesand thereby produce compositions which are more stable than thepolyaldehydes alone and consequently more useful.

It is a more particular object of the invention to provide novelpolyaldehyde compositions which are stabilized against the degradativeeffects of heat.

These and other objects and advantages of the invention which willbecome apparent from the following description thereof are accomplishedby incorporating in or ice wherein R can be the same or different andare selected from the group consisting of hydrogen, the halogens, aminoand nitro radicals, and alkyl, alkenyl, alkoxy and aryl radicals havingup to 16 carbon atoms, and R is selected from the group consisting ofhydrogen, the halogens, amino and nitro radicals, alkyl, alkenyl, alkoxyand aryl radicals having up to 16 carbon atoms, and radicals of theformula SR" wherein R" is selected from the group consisting ofmorpholiny-l and alkyl-substituted morpholinyl radicals. Examples ofsuitable compounds conforming to this formula include benzothiazole,

Z-chlorobenzothiazole, Z-methylbenzothiazole, Z-butylbenzothiazole,2-dodecylbenzothiazole, 2-ethoxybenzothiazole, 2-phenylbenzothiazole,2-viny lbenzothiazole, 2-nitrobenzothiazole, Z-benzylbenzothiazole,2,5-dimethylbenzothiazole, 2,5,6-trimethylbenzothiazole,2-amino-4-rnethylbenzothiazole, 2-an1ino-6-methylbenzothiazole,5-amino-2-methylbenzothiazole, Z-chloro-6-methylbenzothiazole,6-iodo-2-methylbenzothiazole, 5-amino-6-methoxy-2-methylbenzothiazole7-amino-4-ch-loro-Z-ethylbenzothiazole, Z-methyl-S-nitrobenzothiazole,S-nitrobenzothiazole, 2-chloro-6-nitrobenzothiazole,2,S-diamino-6-nitrobenzothiazole, 2amino-6-ethoxybenzothiazole,2-ch-loro-4-methoxybenzothiazole, 5-amino-2,6-dimethoxybenzothiazole,5-amino-2-ethoxy-6-methoxybenzothiazole, Z-amino-6-bromobenzothiazole,2-amino-6-phenylbenzothiazole, 6-ethoxy-Z-phenylbenzothiazole,2-ethyl-6-phenylbenzothiazole, S-chloro-2-phenylbenzothiazole,6-amino-2-phenylbenzothiazole, 2- 2,6-dimethyl-4-morpholinothio-benzothiazole, 5-ch1oro-2-(2,6-dimethylmorpholinothio)-benzothiazole,

and the like.

The amount of stabilizer used can be varied widely depending upon theparticular polyaldehyde to be stabilized and the degree of stabilizationdesired. Generally, amounts from as little as 0.01% by weight to as muchas 20 to 25% by weight of the polymer can be employed. For mostpractical purposes, amounts from about 0.01% to about 15% aresatisfactory with amounts from about 3 to about 6% being preferred.

The stabilizer compounds can be incorporated in the polymer in any ofseveral ways. Generally, they are added by intimately admixing asolution of the stabilizer in a volatile solvent with the finely dividedpolymer and thereafter evaporating the solvent, preferably under reducedpressure. As an alternative method, both the polymer and the stabilizercan be dissolved in a common solvent and the solvent then evaporated.Or, a mutual solution of the stabilizer and the polyaldehyde can be madeand the polymer then precipitated from the solution by addition of wateror some other non-solvent for the resin and stabilizer. Also, theadmixture may be effected by dry blending of the stabilizer and thepolymer on mill rolls. In still another method, the stabilizer can beadded to the polymerization system before or after the polymer hasformed but before isolation of the polymer.

The polyaldehydes which can be thermally stabilized according to theinvention with benzothiazole or a derivative thereof include all thoseobtained by polymerization of aldehydes of the formula R-CHO wherein Rcan be an alkyl, a cycloalkyl, an alkenyl, an alkynyl, an aryl, anaralkyl, or an alkaryl radical. The stabilizers are particularly usefulwith polyaldehydes derived from saturated aliphatic aldehydes containingfrom 2 to carbon atoms and more especially from 2 to 7 carbon atoms.Specific examples of suitable aldehyde monomers include acetaldehyde,propionaldehyde, butyraldehyde, valeraldehyde, heptaldehyde, and thelike; acrolein, methacrolein, substituted methacroleins such as tiglicaldehyde, crotonaldehyde, and the like; propargyl aldehyde;benzaldehyde, p-tolualdehyde, p-isopropylbenzaldehyde, cinnamaldehyde,phenylacetaldehyde, and the like. Other polyaldehydes with which thestabilizers are also useful include those derived from dialdehydes suchas glyoxaldehyde, succinaldehyde, malealdehytde, glutaraldehyde, and thelike; substituted aldehydes such as chloral, aldol, and the like; andheterocyclic aldehydes such furfural and tetrahydrofurfural. Thestabilizers of the invention are likewise useful with copolymersprepared by copolymerizing the foregoing aldehydes with each otherand/or with oxy-aldehydes, ether-aldehydes, amino-aldehydes andhalogenated aldehydes or with other polymerizable vinyl monomers,epoxides, ketones, and the like.

The compositions of the invention may also include, if desired,plasticizers, fillers, pigments, anti-oxidants, and other stabilizerssuch as stabilizers againnt degradation caused by ultra-violet light.

The following example is presented to illustrate the invention but isnot to be construed as limiting it in any manner whatsoever. Theproperty of thermal stability which is used in evaluating the effect ofthe polyaldehyde stabilizers is defined by the value of the reactionrate constant for the thermal degradation of the polymer at a particularelevated temperature, namely, 190 C. It is well known that chemicalreactions may be classed as first order, second order, third order,etc., depending on the number of molecules which enter into or areformed by the reaction. It is also known that the decomposition ordegradation of a material following a first order reaction can beexpressed mathematically in the form of differential equation:

f% =kw in which t is the elapsed time from the beginning of thedecomposition reaction, w is the weight of the material which remainsundecomposed at time t, and k is a rate constant for the equation. Thethermal degradation of the polyaldehyde polymers of this invention hasbeen found to conform generally to a first order reaction which can beexpressed by the above equation. The value of k in this equation,therefore, is utilized to characterize the polymers with respect tothermal stability. The lower the numerical value obtained for thisconstant, the more stable is the polymer.

Example Polypropionaldehyde was prepared by polymerizing propionaldehydeat a temperature of 76 C. in n-hexane as the reaction medium and in thepresence of about 9.8% by weight (based on propionaldehyde) oftriethylaluminum as catalyst. Portions of the polymer were thenstabilized with benzothiazole, Z-aminobenzothiazole, and2-(2,6-dimet.hyl 4 morpholinothio)-benzothiazole and subjected to astabilization test. The procedure for stabilizing and testing was asfollows:

A weighed portion of the polymer was placed in a tared 25-cc. Erlenmeyerflask. Toluene (1 cc.) was added to the flask and the polymer wasallowed to swell for about 3 hours. A solution of the benzothiazole, 2-aminobenzothiazole, or 2-(2,6-dimethyl-4-morpholinothio)-benzothiazolein toluene of a concentration such as to yield upon drying the desiredpercent by weight of the stabilizer was then added and the polymer wasallowed to soak therein for about 3 hours. At the end of this time, thesolvent was evaporated at 25 C. under vacuum. The flask was then purgedfor about five minutes with argon at a rate of about 250 cc. per minute.The argon flow was reduced to about 5-10 cc. per minute and the flaskwas immersed in an oil bath maintained at il C. for fiive minutes whilethe argon purge was maintained at the slow rate. At the end of thistime, the flask was removed from the bath, cooled under argon andweighed to determine any loss in weight. From the Weight loss, thepercent residue was determined. The first order rate constant, k, wascalculated from the data obtained.

For comparative purposes, a sample of polymer containing no stabilizerwas subjected under an argon atmosphere to the elevated temperatures ofthe oil bath along with the stabilized samples and the k value of itsthermal degradation was determined in the same manner.

Also, for comparison, k values of a control sample and a samplecontaining 6% by weight of 2-arninobenzothizaole were determined in air,i.e., no argon purge was employed in the stabilization test. Results ofthese tests which are presented in the following table demonstrate thatthe polyaldehyde compositions of the inventions are outstanding in theirresistance to degradation and deterioration at elevated temperatures.

knm Benzothiazole swlgigizer (Percent by Air 6% benzothiazole 0. 6%Z-aminobenzothiazole 0.

6% 2-(2,6-dimethyl-4-morpholinothi0)- benzothizole wherein R is selectedfrom the group consisting of hydrogen, the halogens, amino and nitroradicals, and alkyl, alkenyl, alkoxy and aryl radicals having up to 16carbon atoms, and R is selected from the group consisting of hydrogen,the halogens, amino and nitro radicals, alkyl, alkenyl, alkoxy and arylradicals having up to 16 carbon atoms, and radicals of the formula SR"wherein R" is selected from the group consisting of morpholinyl andalkyl-substituted morpholinyl radicals.

2. A thermally-stabilized polymeric composition comprising a highpolymer of an aliphatic saturated aldehyde having from 2 to 10 carbonatoms and from about 0.01% to about 15% by weight of said polymer of acompound having the formula wherein R is selected from the groupconsisting of hydrogen, the halogens, amino and nitro radicals, andalkyl, alkenyl, alkoxy and aryl radicals having up to 16 carbon atoms,and R is selected from the group consisting of hydrogen, the halogens,amino and nitro radicals, alkyl, alkenyl, alkoxy and aryl radicalshaving up to 16 carbon atoms, and radicals of the formula SR" wherein R"is selected from the group consisting of morpholinyl andalkyl-substituted morpholinyl radicals.

3. A thermally-stabilized polymeric composition comprisingpolypropionaldehyde and from about 0.01% to about 15% by weight of saidpolypropionaldehyde benzothiazole.

4. A thermally-stabilized polymeric composition comprisingpolypropionaldehyde and from about 0.01% to about 15 by weight of saidpolypropionaldehyde of 2- aminobenzothiazole.

5. A thermally-stabilized polymeric composition comprisingpolypropionaldehyde and from about 0.01% to about 15 by weight of saidpolypropionaldehyde of 2- (2,=6-dimethyl-4-morpholinothio)-benzothiazole.

References Cited by the Examiner UNITED STATES PATENTS 2,376,354 5/ 1945Gresham 260-2 2,983,726 5/1961 Hendry 260-306 3,025,269 3/1962 Calfee26045.9 3,049,509 8/ 1962 Hardy et a1 260-458 3,079,366 2/1963 Hoyle etal. 26045.9 3,112,291 11/1963 Anderson 26045.8 3,131,165 4/1964 Hermannet al. 260'45.9 3,150,130 9/1964 Hardman 260306 FOREIGN PATENTS 108,0957/ 1958 Pakistan.

OTHER REFERENCES Furukawa et al.: Polymerization of Aldehydes andOxides, Interscience Publishers (1963), pages 4, 138, 239, 240, and 241relied on. (Copy available in Scientific Library, QD 281. P6F8.)

LEON I. BERCOVITZ, Primary Examiner.

F. MCKELVEY, Assistant Examiner.

1. A THERMALLY-STABILIZED POLYMERIC COMPOSITION COMPRISING A POLYALDEHDEAND FROM ABOUT 0.01% TO ABOUT 15% BY WEIGHT OF SAID POLYALDEHYDE OF ACOMPOUND OF THE FORMULA